Method of making a thermopile



y 9, 1961 M. K. BLANCHARD 2,983,031

METHOD OF MAKING A THERMOPILE Filed May 7, 1956 IN TOR. MELBOURNE K. B NCHARD METHOD OF MAKING A THERMOPILE Melbourne K. Blanchard, Shorewood, Wis., assignor to A. O. Smith Corporation, Milwaukee, Wis., a corporation of New York Filed May 7, 1956, Ser. No. 583,083

7 Claims. (Cl. 29-1555) This invent-ion relates to. a method of making a series connected thermopile by coating dissimilar metals on a strand of insulating material.

.An object of the invention is to provide an improved process for making thermopiles having a large number of thermoelectric junctions and having increased sensitivity.

According to the invention, a' glass fiber strand, or a strand of other dielectric material, is wound around a mandrel in a generally helical pattern with each turn of the windings spaced from adjacent turns. While supported on the mandrel one-half of the length of each turn is coated with a metal by dipping, spraying or the like, and subsequently, the remaining half of the length of each turn is coated with a second and dissimilar metal. The second metal overlaps the first metal to provide a series of spaced thermoelectric junctions extending throughout the length of the helically wound strand.

The metal coated strand is then removed from the mandrel and connected in an electrical circuit to provide a multi-junctin thermopile.

The present invention provides a simple and inexpensive method of producing a series-connected thermopile having a large number of junctions. As the metal coating on the strand is relatively thin, the heat loss from the junction by conduction through the metal will be decreased and this results in a greater heat differential between the hot and cold junction and a more eflicient thermopile.

In. addition the nominal resistance of the thermopile is high and therefore the output signal may be detected by a circuit having a high input impedance, such as a conventional electronic amplifier.

The drawings illustrate the best method presently contemplated of carrying out the invention.

In the drawings:

Figure 1 is a perspective view of the mandrel with the glass fiber wound thereon;

Fig. 2 is a schematic view of a portion of the length of the turns of the fiber being coated with a metal;

Fig. 3 is a view similar to Fig. 2 showing the remaining portion of the length of each turn being coated with a second and dissimilar metal;

Fig. 4 is a perspective view of the thermopile of the invention asremoved from the mandrel;

Fig. 5 is a perspective view of the compressed helix and having an insulating coating thereon; and

Fig. 6 is an enlarged section showing metal coating.

In constructing the thermopile of the present invention, a glass fiber strand 1, or a strand of a suitable dielectric material, is wound around a generally cylindrical mandrel 2 in a spiral pattern to form a helix. Each turn or convolution of the helix is spaced from adjacent turns to provide a substantial gap 'therebetween.

The outer surface of mandrel 2 is provided with a series of longitudinal extending serrations 3 and the strand 1 is supported on the outer edge of the serrations 3 to provide a series of line contacts between the strand 1 and the mandrel 2, as best shown in Figs. 2 and 3.

To provide a plurality of thermoelectric junctions throughout the length of the strand 1, the mandrel and the helix are dipped into a bath of a molten metal or alloy 4 contained within a trough 5 or the like. As shown in Fig. 2, the mandrel is dipped into the metal 4 such that approximately the lower longitudinal half of the mandrel is immersed in the metal, thereby coating about one-half of the length of each of the turns of strand 1 with the metal. The serrations 3 permit the metal 4 to llow behind the strand and coat the greater portion of the inner surface of the strand, with the exception of the portions contacting the edges of serrations 3.

The metal or alloy 4 employed in the bath may be any metal having a melting point lower than the transition temperature of strand 1 so that the strand will not deform or be decomposed by the heat of the metal. With the use of a glass strand, metals such as lead, tin, bismuth and zinc can be employed.

After approximately one-half of the length of each turn of strand 1 is coated, the mandrel is removed from the bath and the metal coating 6 is allowed to solidify. The mandrel is then placed in a second trough 7 containing a metal 8 dissimilar from metal 4. Under this step of the invention the uncoated half of the mandrel is dipped in the metal 8 so that the uncoated portion. of each turn of the strand 1 is coated with metal and the metal coating 9 overlaps the end portions of the coating 6 on each turn to provide a series of thermoelectric junctions 10 which are disposed in spaced relation throughout the length of the strand. -The helix is, in effect, a series of sections of the metal coating 6 alternating and electrically connected to a series of sections of the metal coating 9 and extending substantially the length of the helix.

The, mandrel is then removed from the trough 7, and the coated strand withdrawn from the mandrel. The terminals or ends of the metal coated strand are then connected by leads 11 in an electric circuit, as shown in Fig. 4, to provide a simple and efficient thermopile unit. The element 12 shown in Fig. 4 is a diagrammatic representation of an electrical device such as a relay winding, a detection apparatus or a source of power of the thermopile is operated to develop a differential in temperature.

The electromotive force of the thermopile can be varied by varying the number of thermoelectric junctions, by changing the metals used, or by coupling with other thermopiles.

While the above description is directed to. coating the strand 1 by dipping in a metal bath, it is contemplated that the strand may be coated with metal by other processes such as spraying, sputtering or vacuum plating. In these methods of coating, it may be necessary to mask the portion of the strand not to be coated in order to obtain the separate and alternate coatings 6 and 9 of dissimilar metals. By using spraying, sputtering or vacuum plating higher melting metals such as constantan, copper, iron, chromel and alurnel can be employed as the metal coatings 6 and 9.

It is also within the scope of the inventionto employ a smooth surfaced mandrel 2 instead of the serrated mandrel. With the use of a smooth mandrel, the inner surface of the strand 1 would be uncoated, but the electromotive force developed by the thermopile can be maintained by increasing the thickness of the coating on the outer surface of the strand.

The thermopile of the invention can be used in the helical form in which it is removed from the mandrel, or it can be bent into a single straight thermopile unit if the ductility of the metal permits bending, or it can be compressed in helical form into a dense compact unit as shown in Fig. 6. If compressed in helical form, the coating sections 6 and 9 are insulated from each other by applying a layer 13 of rubber, plastic or wax or the like to the thermopile. In this situation the thermoelectric un ti ns {are preferably masked; to: prevent om eir i coa tedwith the nsulat'n g As a glassifiber strand; can be ade with' a very} small diameter or cross-sectional ai ea and oonsid er a rhgi sena les riger number ofgjunc v I entrate'd in I :g, en area; and in etteet creases: the electrniotive tore developed by the? thereto carrying on t the invention are con templated as being within the scope of the following claims 3 particuiarly poi 5; :out and: d stin y a m n I the subject matter which is regarded :as the invention. i

g a strand 1 of? inulati' e for'm ofa eljix spac the. length; of; each turn different: from; said first win reiationu te junction 13 :forme it each 5mm; retire in 1g the terminals? of the heflixiin an: electrical; revgi e a series onnectedithermopilei therein j 5 h d a n i km th m a teiw w trend :of insulating material around a mandrelh of; generally longitudinal gridgje'sg xtgending;

T i'phrynsreet re iss-61a, a; ating: sub- :h it at the: Eengt of each and with {a metal mocoxiple junction on e'a' the mana er; and connecting the terminals. 1 i in an electrical circuit to provide a: series: connected thermdpile tlterein. r I i'flzfv i i i i-i j 3 A inethoido mak gathermopile, comprisingwind ing a strand of'die le'ctric'mate'r'ial around'a' mandrel in the form of a helix, spacing each turn of the helix from adjacent turns to provide a gap therebetween, coating a portion of the length of each turn with a metallic ma-r terial, coating the remaining portion of the length of each turn with a second metallic material diiferent from said first metallic material and lapping the second metallic material over the ends of the first metallic material on each turn to provide a thermocouple junction on each turn, removing the helix from the mandrel, coating the metal covered helix with a flexible insulating material while masking the electrical junctions to prevent said insulating material from coating said junctions, compressing the helix lengthwise to bring the turns into substantially contiguous relation, and connecting the ends of the helix in an electrical circuit to provide a series connected thermopile therein.

4. A method of making a thermopile, comprising winding strands of glass fiber in the form of a helix, spacing each turn of the helix from adjacent turns to provide a A= ui oie ot making a-thetrriopile, comprising' wise I the? lwrmmehemtnarei, and

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betwe n,

coat Ea portion of thelengtl ee ond molten; metall c mater I lectricgpropertiesj than 5 the gfir I with said second metallic material? and lappln gsaid se ded;

gmaterial @8761: the ends t the first; metallic, ma?

1 action 1 ea tam? w pro'i e a thermoe up n each. um; and p0 um t; the ends; of; the; :lelix:

therein. 1 I

' strandgof dielectric material around a; mandate hava t n w l f the; me alli icoajtin Wid . ethoi efim iasi i pfle some hing strand? of dielectric material around a mandre s: n l wa venfi to bring the turns into substantially continguous relation, and connecting the ends of the helix in an electrical circuit to provide a series connected thermopile therein.

7. A method of making a thermopile, comprising winding a strand of glass fibers in a generally helical pattern with each turn of the helix being spaced from adjacent turns, coating a portion of the length of each turn with a first metal, coating a second portion of the length of each turn with a second metal diiferent from said first metal and in overlapping relation with the ends of the first metal on each turn to provide a thermocouple junction on each turn, and connecting the ends of the helix in an electrical circuit to provide a series connected thermopile therein.

References Cited in the file of this patent UNITED STATES PATENTS I t n 1 electrical circuit to provide 'sjer iesconnected thermopile;

, 5 v 5 I A'rirtetliodpf making a thermopi e,;compr ising vvind-:

i t: zing a: series ;of I generjallyj longit dana spa'ced iareun'd the: periphery thereof I ppi g the hel eaten L ed Q a? th am 2 ing =material; While tnaintaiuiirig the electrical junctions I between said first and secenqii metallic: material flee of: said insulating material, compressingthe helix lengthwise 

